Round Corners Plugin Error Message - Corner at Fault

I’ve installed Round Corners and have read what information I can find so far regarding using it. I am trying to round the top face (edge) of a “can” if you will (a cylinder without a top and empty inside). I have tried both selecting both edges, the face and one edge at a time. Each time I try to generate I get an error message saying the “corner at fault is highlighted in the model” First of all its a cylinder so I’m not sure why it would have corners. But more importantly, does anyone know what this error really means and how do I fix the “corner at fault”? Thank you.

Please share the SKP file